Arc discharge device with entire casing shielded from the arc



Sept 23, 1947- H. wlNoGRAD 2,427,999

ARC DISCHARGE DEVICE WITH` ENTIRE CASING SHIELDED FROM THE ARC Filed ont. 24, 1942 2 sheets-sheet 1 Sept. 23, 1947. H. wlNoGRAD ARC DISCHARGE DEVICE WITH ENTIRE CASI'NG SHIELDED FROM THE ARC 2 Sheets-Sheet 2 Filed opt. 24. 1942 Patented Sept. 23, 1947 ARC DISCHARGE DEVICE WITH ENTIRE CASING SHIELDED FROM THE ARC Harold Winograd, Milwaukee, Wis., assigner to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application October 24, 1942, Serial No. 463,167

(Cl. Z50-27.5)

25 Claims. e l

This invention relates in general to improvements in vapor electric devices, and more particularly to means for controlling the course of the arc and the flow of vaporized conductive medium in arcing devices of the single anode type of high current carrying capacity.

To enable a single anode vapor electric device of high current carrying capacity to operate satisfactorily, it has been found necessary to control the vapor density within the different portions of the device and to maintain the temperature of the different elements of the device within predetermined limits. In particular, in valves of the vaporizable liquid cathode type it is generally necessary to shield the cathode against heat radiation from the anode to prevent the cathode surface from reaching a temperature resulting in vaporization of the cathode material at an excessive rate. A baille inserted between the anode and the cathode may provide for this shielding and at the same time guide the course of the arc within the device.

As the bale is subjected to considerable heat radiation it has been proposed to utilize baiiles of the water cooled type. Such bailles are, however, disadvantageous in that vaporized cathode material condenses thereon and thereby disturbs the operation of the device. On the other hand an v uncooled baille reaches such a temperature as to re-radiate a considerable amount of heat towards the cathode. This disadvantage may be obviated by providing a second baiile to intercept the radiation between the iirst baille and the cathode.

In general it is preferable to provide single anode vapor electric devices with a continuously excited cathode of a suitable known type rather than a cathode of the intermittently excited type. When the casing of the device is made of metal it is advantageous not to insulate such cathode from the casing to simplify the design of the casing and reduce its cost. The tendency of the arc is then frequently to attach to the casing wall rather than toi the cathode. may be overcome by providing suitable shielding means between the path of the arc and the casing. `Such shielding means may be made of conductive material and may be water cooled to control the temperature of the device and to condense material vaporized from the cathode when the cathode is of the liquid type.

The shielding means need not form a solid surface but must not present gaps of such size as to be pervious to arcing between the anode and the casing. The shielding means must also be joined to the anode and to the cathode in arc This disadvantage Y impervious relation, preferably through suitable insulating means. When the device is provided with a control grid, the baffles and the shield inserted in the device also preferably cooperate with the anode to conne the grid within as small a space as is found possible to reduce the time necessary for the deionizing action of the grid. Inner conductive elements of the device between which deleterious arcing is apt to take place should be conductively interconnected wherever this is feasible.

It is therefore one of the objects of the present invention to provide a vapor electric device of the single anode type inV which the cathode is adequately shielded against heat radiation from the anode without undesired condensation of vaporized cathode material.

Another object of thepresent invention is to provide a vapor electric device of the single anode metal enclosed type in which arcing between the anode and the casing isprecluded without insulating the cathode from the casing.

Another object of the present invention is to provide a vapor electric device in which a control grid is conned within a reduced space removed from the blast of material vaporized from the cathode by the arc.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing in which:

Fig. l is a view in vertical cross section through a vapor electric device in which transverse baffles are mounted on an insulated cooling coil serving to shield the casing against arcing from the anode;

Fig. 2 is a view in cross section through line II-II in Fig. 1 and showing the baffles of the cathode water jacket of the embodiment illustrated in Fig. 1 and Fig. 3 is a partial view in vertical cross section through a vapor electric device in which the baiiles are suspended from the control grid in insulated relation thereto.

Referring more particularly to the drawing by characters of reference, the device illustrated in Fig. 1 comprises a casing 6 which is herein assumed to be made of conductive material such as steel. Casing 6 comprises a cylindrical side wall l and a disc shaped bottom wall portion 3. Cylinder 'l is provided with a ilange 9 adapted to support the edge portion of a disc shaped cover ll. The cover and the liange are sealed in gas tight relation by means of a gasket l2 of suitable material such as rubber, which is maintained under pressure by the screws (not shown) fastening the cover to the flange. Cover II and cylinder 1 are conductively connected by the screws and by direct contact along the side walls of the groove containing gasket I2.

Cover II denes an aperture which is axially located with respect to cylinder 1 and which is adapted to receive an insulating member such as a* porcelain bushing I3. The bushing is supported on the cover II by means of a ring I4. To fasten ring I4 to the cover, the cover is provided with a plurality of tapped recesses I6 exposed to the interior of the casing. Each recess receives a screw I1 which incompletely fills the recess and thereby entraps some air within the recess. This air may be removed by the usual evacuatingmeans provided for the device through a passage such as an axial passage I8 provided in screw I1.

Bushing I3 is sealed in gas-tight relation against cover II by means of a suitable seal such as a mercury seal I9. A current conductor 2I extends through-bushing I3 and is Vsealed thereagainst in gas-tight relation by means of the blind sleeve 22 and a mercury seal 23. Conductor 2l is screwed vinto the tapped bore of sleeve 22 and the space therebetween is vented to the interior of casing 6 through a passage 24. Sleeve 22 may be provided with a iinned radiator 25.

The device isl provided with a single main anode 26 of substantially cylindrical contour preferably made of graphite. The anode is made in two parts assembled by screw threads, the upper anode portion being clamped between the portion of conductor 2I extending into casing 6 and bushing I3 by means of a spring 21.

The cathode 28 of the device preferably consists of a pool of vaporizable conductive material such as mercury disposed in the bottoml portion 8 of the casing in conductive relation thereto. As a result of the above described arrangement -of parts, anode 28 is supported axially in casing 6 above cathode 28 in insulated relation with the casing and with the cathode.

A control electroder29 of the grid type is arranged in close proximity to the anode to control the iiow of current between the anode and the cathode. Grid 29 is preferably made of graphite and is preferably so shaped as to follow the contour of anode 2B. The grid may be suspended from bushing I3 in arc impervious relation thereto by means of a ring 3l and may receive control potentials through a connection 32 penetrating cover II in insulated and gas-tight relation thereto. Grid 29 preferably comprises a disc shaped perforated wall 33 facing cathode 28 and a cylindrical perforated wall 34 facing cylinder 1.

In order to prevent arcing between anode 26 and casing 6, shielding means are disposed within the casing about anode Y26, grid 29 and the space between the grid and cathode 28. The shielding means may consist of a water cooled coil 35 of conductive material such as steel, or copper covered with steel. Coil 35 preferably comprises two identical coil sections of tubing, of which one consists of a helically wound intermediate portion 33 having a pitch, equal to` slightly more than twice the diameter of the tubing with an upper end portion 31 and a lower end Yportion 38both arranged on the left hand side of thegure with their axes substantially in the plane of section. The other section of tubing similarly consists-of` a helically wound intermediate portion 39 with an upper end portion 40 and a lower end portion 4I.

Helical portions 36 and 39 have their turns interleaved, and the vend portions 40,.,4I are relation thereto.

substantially diametrically opposed to end portions 31, 38. End portions 38, 4I issue into a header 42 connecting the two tubing sections in series. Header 42 is preferably of toroidal sh'ape, consisting of a section of tubing which is bent circularly, after which its ends are welded together. Coil 35 is suspended from cover II through tubing portions 31, 4D, which are heldin the cover in gas-tight and insulated relation thereto. Tubing portion 31, for example, is held in cover II through a rubber gasket 43 which is compressed by screws 44 through a sliding flange 46 and a pair of insulators 41, 48. Adjacent turns of helical portions .36, 39 may be joined by tack welds to increase the rigidity of the cooling coil.

Coolingcoil 35is so wound that adjacent turns of the helical portions thereof deiine a gap which is pervious to the flow of vaporized cathode mercury and of incondensable gases but is impervious to arcing between the anode and the casing. The designation of the coil as impervious toarcing is intended to ,means that arcing from the anode to the casingthrough the interstices betweenadjvacent turns ofthe coil does not take placeas long as thedevice is properly conditioned and is connected in a circuit operating under the intended conditions of voltage and .cur-

rent. As is welllrnown, it is not feasible to de-- termine mathematically the dimensions to be given t0 a structureofthe type of coil 6 to render` it impervious toarcing. The maximumA spacing between adjacent turns for given operating conditionsV therefore cannot be specified and must be determined 4by experiment.

When the cooling Ycoil cannot be made to extend in close proximity to the anode and to the cathode, it may be aided inV its arc preventing action by insulatingrmea'ns ldisposed between the anode and the coil in arc impervious relation thereto and other insulating means, disposed between the cathode and the coil in arc impervious On the Vanode side, bushing I3 cooperates with a cylindro-conical sheet metal shield 49 tovprevent arcing between the anode and the casing above the uppermost turn of coil 35.

On the cathode side, a ring shaped insulator 50 is immersed in the cathode to limittheattachment ofthe arc to the central portionof the cathode. Insulator 50 is kconnected with coil35 in arcimpervious relationthereto by v-means of an annular structure comprising a p air of shields 5I, ,52 mounted on V.a gutter shaped ring 53. Shieldsl and52 and ring53 also serve to co1- leCt mercury condensed on coil 35 and to return it tothe central `portion of cathode 28. vThe Vcondensed mercury may occasionally drop from Shield.

If cooling coil 35 andshield 5I were unconnected byv a mercury stream or otherwise, they would tend to assume diiferent .potentials because they-are immersed in-mercury vapors of different densities and in different states of ionization. `Whena stream of mercury therebtween breaks, a small arc may result and establishza cathode spot on shield 5I. The main arc may then divide itself into two portions, one of which extends from anode -26 to shield 5I, vand `the other from ring-53 -to cathode 28, and thereby cause serious damage to shields 5I, 52 and to ring 53. This abnormal operating condition is avoided by conductvely connecting shield 5I with header42 through leaf springs.

d Ring 53 is mounted on another ring -55 through insulated bolts 56. Ring 55 rests on the bottom portion 8 of the casing and thereby reduces the amount of mercury required to maintain the cathode at the 'desired level. Insulator 50 is urged againstvring 53 by springs '51 through a sheet metal ring 58. The central portion of casing bottom 8 may be raised above the level required for the insertion of ring 58 to further reduce the amount of mercury required in the cathode,

Header 42 supports an annular baille 59 through a plurality of metal straps 68. Bailles 59 extends within coil 35 across the peripheral region of casing 6 in close proximity to grid 29 between the'grid and the cathode. The baille cooperates with anode 26 and with coil 35 to conne a space following substantially the contour of grid 29. The baille also cooperates with coil 35 to control the ilow of mercury vaporized from cathode 28 by deilecting the mercury vapor from the peripheral portion of grid 29 toward coil 35.

Baille 59 supports a lenticulal bailling device comprising a pair of disc-shaped graphite bailles 6|, 62 through suitable metal bolts 63 shielded from the arc by refractory insulating bushings 10. Bailles 6|, 62 are substantially coextensive and are disposed transversely across the central region of casing -6 between anode 26 and cathode 28. Baille 6| serves to shield cathode 28 against heat radiation from anode 26 and is cooled substantially entirely by radiation toward the other members of the device. Baille 62 shields cathode 28 against 1re-radiation of heat from baille 6|. Bailles 6|, 62 also cooperate with baille 59 to define a sinuous path for the arc between anode `26 and cathode 28 and to deilect mercury vaporized from cathode 28 away 4from grid 29 and towards coil 35. The upper surfaces of bames 59, 6| are preferably inclined to cause return to the cathode of any condensed mercury that may drop or `form thereon during operation or during shut down of the device.

Baiiles 6|, 62 are conveniently joined along their edges, and at least one of the bailles may be dished to leave a space between the bailles for impeding the transfer of heat from baille 6| to baille 62. The space between the bailles may contain a barrier of heat insulating refractory material 45 to further impede such transmission of heat. Baille 62 may support a graphite ignitionexcitation anode 64 through an insulating bushing 65. Anode 64 may receive current through an insulated connection 66 penetrating through cover in insulated and gas-tight relation thereto.

For igniting an arc at cathode 28 a jet of mercury may be projected against anode 64 by means of a nozzle shaped piston 61 of magnetic material movable in a cylinder 68 welded to casing bottom portion 8. Piston 61 may be actuated by means of a solenoid 69 energized -from a suitable source.

Cathode 28 is cooled by circulation of water through a water jacket 1I applied to casing bottom portion 8 in fluid-tight relation thereto and provided with connecting nipples 12, 13. rThe cooling water is guided in a circuitous path through the water jacket by means comprising a substantially radial baille 14 and a plurality of coaxial annular baffles 15, 16, 11 welded to jacket 1|. As shown in Fig. 2, each annular baille extends from one face of baille 14 to a point in jacent'annular bailles such as 15,16 extend from 6 opposite faces of baille 14. The bailles thus force circulation of the cooling water throughout the water jacket and are much simpler and cheaper to manufacture than the helical bailles heretofore used for that purpose. Jacket 1|is connected in series with coil 35 through a length o insulating hose 18. f

The casing may be evacuated by means of a suitable pumping system (not shown) connected with an outletY 19 provided through the wall of cylinder 1 in close proximity to cooling coil 35.

Anode 26 being connected with a suitable source of current and anode 64 being connected with an auxiliarysource of direct current, both sources being inserted in circuits connected with cathode 28, operation of the device is initiated by supplying a momentary current impulse to solenoid 69. The solenoid attracts piston 61, which imomentarily projects a jet of cathode mercury against anode 64. Current then flows between anode 64 and cathode 28 through the jet and, when the jet is broken, a continuous arc is established between anode 64 and cathode 28. A cathode spot is thereby maintained at the cathode and the cathode remains continuously emissive.

In general, anode 26 is required to carry periodic current impulses under the control of grid 29. Each current impulse is conducted by an arc established between anode 26 and cathode 28 through the mercury vapor contained within the device. The arc passes principally through the apertures of grid portion 33 and follows' the sinuous path dened by bailles 59, 6|, 62 and coil 35 to the cathode. The flow of current -raisesthe anode temperature in relation to the current intensity but radiation from the anode to the cathode is intercepted by bailles 6|, 62. Cooling of the anode is facilitated by the apertures through grid portion 34, through which the anode may radiate directly towards coil 35.

The ilow of water through jacket 1| maintains the cathode temperature within the desired limits. The water issuing from the jacket flows through nipple 12, insulating hose 18 and coil 35. The electrical resistance of the water co1- umn contained within hose 18 is very high compared to the resistance of the arc s0 that there is no tendency for the arc t0 attach to the cooling coil or to the bailles to conduct current to the cathode through the coil and the water contained in hose 18. In spite of the presence of water in hose 18 coil 35 may therefore be considered to be substantially insulated from cathode 28.

The upper portion of coil 35 removes heat radi- 'ated thereto by anode 26 and grid portion 34. The lower portion of the coil removes heat radiated from the arc and condenses vaporized mercury directed thereagainst by bailles 59 and 62. The arrangement of bailles 59,A 6| and coil 35 reduces to a minimum the space, in which the grid collects the charges of the vapor ions. The bailles and the cooling coil also operate to reduce the vapor density in such space. Both actions contribute to reduce the amount of vapor that the grid is required to deionize after each operating period of the anode 26 and thus lessen the time required for the grid deionizing action.

The cooling coil prevents arcing between anode 26 and any portion of casing 6 because of the relatively close spacing of adjacent turns of the helical portion thereof. The mercury vapor however may pass between the turns of the cooling coil tol reach the outside surface of the coil and condense thereon. The entire area of the 'll coiljis thus available for condensing vapor-ized mercury.

Noncondensable gases may be removed from casing 6 through outlet 19. Because of the location of the outlet in close proximity to coil 35 the density of the mercury vapor at the outlet is very low and the removed gases are substantially free of Vaporized mercury.

In the embodiment partially illustrated in Fig. 3 grid portions 33, 34 are shown as built separately and as assembled by means of bolts 8|. Baiiie 59 is suspended from the grids in insulated relation through bolts 8i and refractory insulators 82. Depositionof conductive material on the entire surface of insulators 82, which would lead to undesired electrical connection between grid 29 and baille 59, is prevented by suitable refractory shielding means arranged adjacent at least part of the exposed areas of insulators 82. Such shielding means may include shirted insulators 83 and insulating caps 8d. Bolts 63 may also be protected against the action of the arc by bushings 10 and insulating caps 85.

In the present embodiment the cooling coil is applied to the external surface of casing l. A shield between the anode and the casing may again be provided if the cathode is continuously emissive and is not insulated from the casing. The shield may be omitted as shown in Fig. 3 when the cathode is intermittently emissive orv is insulated from the casing.

Although but two embodiments of the present invention have been illustrated and described it will be apparent to those skilled in the art that variousV changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A vapor electric device comprising an evacuated casing, an anode and a pool of vaporizable conductive material serving as cathode in said casing, and a lenticular baiiling device extending transversely across said casing between said vanode and said cathode comprising a first baille for shielding substantially the entire surface of saidcathode pool against heat radiation from said anode, a second baille coextensive with said iirst baille for shielding substantially the entire surface of said cathode pool against heat radiation from said first baille, and a barrier of heat insulating material inserted between said bailles for impeding the transmission of heat from said iirst baille to said second baille.

2. A vapor electric device comprising an evacuated casing, an anode and a pool of vaporizable conductive material serving as cathode in said casing, a control electrode arranged in close proximity to said anode, and baille means disposed across said casing in close proximity t said control electrode between said control electrode and said cathode and cooperating with saidY anode for confining a space following substantially the contour of said control electrode, said baille means extending in such close proximity to said casing as to obstruct the direct flow oi material Vaporized from said cathode pool toward any point of said control electrode.

3. A vapor electric device comprising a pool of vaporizable conductive material serving as cathode, an anode disposed above said cathode pool,

4a control electrode arranged in close proximity space between said control electrode and said cathode pool, and a baille arranged in close proximity to said control electrode between said con-A trol electrode and said cathode pool and cooper.- ating with said anode and with said member for confining a space following substantially the contour of said control electrode, said baille extending in such close proximity to said member as to deflect the direct flow of material vaporized from said cathode pool away from all points of said control electrode and toward said member.

4. A vapor electric device comprising an evacuated casing, said casing comprising metallic parts all in conductive relation to each other, a vaporizable cathode in the bottom portion of said casing in conductive relation thereto, an anode arranged above said cathode within said casing in insulated relation thereto, and means for controlling the flow of material vaporized from said cathode comprising bailling means arranged transversely to Said casing between said anode and said cathode and a liquid cooled member substantially insulated from said cathode and from said casing disposed about said anode, said bafiling means and the space between said bailling means and said cathode, said member shielding al1 the metallic parts of said casing against attachment of an arc thereat.

5. A vapor electric device comprising an evacuated casing, said casing comprising metallic parts all in conductive relation to each other, a vaporizable cathode disposed in the bottom portion of said casing in conductive relation thereto, an anode disposed above said cathode within said casing in insulated relation thereto, and. means for preventing arcing between said anode and all the metallic parts of said casing comprising a liquid cooled coil supported in said casing about said anode and the space between said anode and said cathode in substantially insulated relation to said casing and said anode, adjacent turns of said coil defining a gap pervious to the flow of vaporized cathode material but impervious to arcing, and insulating means disposed between said coil and said cathode in arc impervious relation thereto.

6. In a vapor electric device, the combination of an evacuated casing comprising metallic parts, means connecting all said metallic parts of said casing in conductive relation to each other, a cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all the metallic parts of said casing comprising a. member impervious to arcing supported in said casing between said anode and said casing in substantially insulated relation thereto and means comprising insulating means disposed between said member and said anode and between said member and said cathode to form arc impervious barriers therebetween.

7. A vapor electric device comprisingv a, cylindrical casing, an anode disposed axially in said casing, and a cylindrical cooling coil disposed between said anode and said casing comprising a first section of tubing comprising a helically wound intermediate portion and two end portions arranged with their axes substantially in a predetermined diametre-1 plane, a second section of tubing identical to said nrst section and having the turns of its helical portion interleaved with the turns of the helical portion of said nr'st seetion and its end portions substantially diametrically opposite to the end portions of said iiljst section, and a toroidal header joining a pair of oppositely arranged end portions of said tubing sections.

8. A vapor electric device comprising a metallic container comprising a vertica1 cylindrical portion and a disc shaped bottom portion, a liquid cathode in said bottom portion, and means for cooling said cathode comprising a jacket applied in huid-tight relation to said bottom portion, and means for guiding cooling iiuid in a circuitous path in said jacket comprising a substantially radial baille and a plurality of substantially coaxial annular baiiles, each said annular baille extending from one face of said radial baille to a point in proximity to the other face of said radial baille and adjacent ones of said annular baiiles extending from opposite faces of said radial baille.

9. A vapor electric device comprising an evacuated casing, a vaporizable liquid cathode in said -casing, a rst conductive member arranged within said casing in insulated relation to said cathode and provided with fluid cooling for condensing vaporized cathode material thereon, a second conductive member arranged within said casing in insulated relation to said cathode a relatively short distance below said first member, whereby streams of condensed cathode material may flow from said rst member to said second member, and a conductive connection 'between said members to prevent arcing thereat upon interruption or said streams of condensed cathode material.

10. In a vapor electric device, the combination of an evacuated casing comprising metallic parts, means` connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material serving as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a member forming a path for the ow of cooling fluid therethrough, said member being impervious to arcing between said anode and said casing but being pervious to the ow of material vaporized from said cathode pool to enable said vaporized material to have access to all surfaces of said member to condense thereon, and means comprising insulating means disposed between said member and said anode and between said member and said cathode pool to form with said member an arc impervious barrier between said anode and said cathode pool.

ll. In a vapor electric device the combination 'of an evacuated casing comprising metallic parts,

means connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material serving as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a member pervious to the ilow of material vaporized from said cathode pool but impervious to arcing, and means comprising insulating means disposed between said member and said anode and between said member and said cathode pool to form with said member an arc impervious I:barrier between said anode and said cathode pool.

12. A vapor electric device comprising an evacuated casing, said casing comprising metallic parts all in conductive relation to each other, a pool of vaporizable conductive material serving l0 as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all the metallic parts of said casing comprising a member impervious to arcing supported in said casing between said anode and said cathode pool in substantially insulated and ar-c impervious relation thereto, said member forming a path for the flow of cooling iluid therethrough and being pervious to the flow of material vaporized from said cathode pool, whereby vaporized cathode material may condense on the surfaces of said member facing said casing.

13. A vapor electric device comprising an evacuated casing, said casing comprising metallic parts all in conductive relation to each other, a pool of vaporizable conductive material serving as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all the metallic parts or said casing comprising a member pervious to the flow of material vaporized from said cathode pool but impervious to arcing supported in said casing between said anode and said cathode pool in substantially insulated and arc impervious relation thereto.

14. A vapor electric device comprising an evacuated casing, a pool of vaporizable conductive material of high specic weight in the bottom portion of said casing, an insulating ring partially immersed in said pool to deiine a cathode area thereof, condenser means for condensing material vaporized from said pool, collector means supported on said insulating ring for returning material condensed by said condenser means to said cathode area, a solid ring disposed about said insulating ring, and means for supporting said collector means and said insulating ring on said solid ring to urge said solid ring against said bottom portion of said casing, whereby the material of said pool is substantially entirely conned within said cathode area.

l5. A vapor electric device comprising an evacuated casing, a pool of vaporizable conductive material in the bottom portion of said casing, a ring of insulating material partially immersed in said pool to dene a cathode area thereof, and means for coniining substantially all said material within said cathode area comprising a ring of solid material resting on the bottom of said casing about said ring of insulating material.

16. A vapor electric device comprising an evacuated casing, a pool of vaporizable conductive material in the bottom portion of said casing, a ring of insulating material partially immersed in said pool to dene a cathode area thereof, a iluid cooled member disposed within said casing in insulated relation thereto for condensing material vaporized from said pool, and means for collecting material condensed by said member and for returning the collected materia to said pool by gravity, said means including drip means for directing all said collected material into said cathode area to confine to said cathode area any arcs established between said drip means and said pool upon interruption of a stream of said collected material flowing therebetween.

17. A vapor electric device comprising an evacuated metallic casing, a metallic cover for said casing removably mounted o-n said casing in conductive relation thereto, an anode mounted on said cover in insulated relation thereto, a pool of vaporizable conductive material disposed in the bottom portion o1"- said'casing in conductiverelation thereto, and insulation ring partially imf mersed in said pool to define a cathode area, means for condensing material vaporized from said pool comprising a fluid-cooled coil disposed about said anode and supported on said cover out of contact with said casing, said coil comprising end portions penetrating through said cover in insulated relation thereto, said coil being pervious to material vaporizedV from said pool but impervious to arcing, means for connecting said coil with said anode in insulated arc impervious relation thereto, and collector means in arc impervious relation to said coil and to said ring for collecting material from said .pool condensed by said coil and for returning said condensed material to said cathode area.

18. A vapor electric device comprising an evacuated metallic casing, a metallic cover for said casing removably mounted on said casing in con.. ductive relation thereto, an anode mounted on said cover in insulated relation thereto, a pool of vaporizable Conductive material disposed in the bottom portion of said casing in conductive relation thereto, an insulation ring partially immersed in said pool to dene a cathode area thereof, means for condensing material vaporized from said pool comprising a iluid cooled coil disposed about said anode and supported on said cover outV of Contact with said casing, saidcoil comprising end portions penetrating through said cover in insulated relation thereto, said coil being pervious to material vaporized from said pool but impervious to arcing from said anode to said casing, means for connecting said coil with said anode. in insulated arc impervious relation thereto, and collector means supported on said ring in arc impervious relation thereto for collecting material from said pool condensed by said coil and for returning said condensed material to said cathode area, said collector means comprising means engaging said coil in removable arc impervious relation thereto.

19. A vapor electric device comprising an evacuated metallic casing, a metallic cover for said casing removably mounted on said casing in conductive relation thereto, a pool of vaporizabler conductive material serving as cathode disposed in the bottom portion of said casing in conductive relation thereto, an anode mounted on said cover in insulated relation thereto, a control electrode mounted on said cover in insulated relation thereto and disposed in close proximity to said anode. a fluid cooled coil disposed about said anode, said controlelectrode and the space contained between said control electrode and said cathode, said coil being supported on said cover and comprising end portions penetrating through said cover in insulated relation thereto, said coil being pervious to material vaporized from said cathode pool but impervious to arcing from said anode to said casing, means for connecting said coil with said anode and with said Vcathode in insulated arc impervious relation thereto, and barile means supported on said coil in close proximity to said control electrode and cooperating with said anode and with said coil to conne a space following substantially the contour of said control electrode, said baille means extending in such close proximity to said coil as to deflect material vaporized from said cathode vpool away from all points of said control electrode and toward said coil.

20. A vapor electric device comprising an evacuated metallic casing, a metallic cover for said 12 casing removably mounted on said casing inicoijl-v ductive relation thereto, a pool of VaDOlZable conductive materialdisposed in the bottom portion of said casingv in Vconductive relation there-r Y to, aninsulation ringpartially immersed in said pool to dene a cathode area thereof, an anode mounted on said cover in insulated relation theretodirectly above said cathode area, a control electrode mounted'on said cover in insulated relation thereto in close proximity to said anode, a fluid cooled coil disposedvabout said anode, said control electrode and the space contained between said control electrode and said cathode, said coil being supported on said cover and comprising end portions penetrating through said cover in insulated relation thereto,'said coil being pervious to material vaporized from said cathode pool but impervious to arcing from said anode to said casing, means for connecting said coil with said anode in insulated arc impervious relation thereto, collector means conductively connected With said coil in arc impervious relation to said coil and to said ring for collecting material from said cathode pool condensed by said coil and for returning said condensed material to said cathode area, and baiiie means supported on said coil between said control electrode and said cathode for shielding substantially the entire surface of said cathode pool against heat radiation from said anode and from said control electrode.

21. In a vapor electric device, the combination of a casing comprising metallic parts, means connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material serving as czhode disposedk insaid casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said-anode and all said parts of said casing comprising a member impervious to arcing supported between said anode and said .cathode in substantially insulated and arc impervious relation theretoy said member comprising anelement Ypervious to the flow of material vaporized from said cathode pool and forming a path for the flow of cooling iiuid.

22. In a vapor electric device, the combination of a casing comprising metallic parts, means connecting all the metallic parts of said casing in conductive lrelation* to each other, a pool of vaporizable conductive material serving as cathodedisposedrin said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a member impervious to arcing supported between said anode and said cathode in substantially insulated and arc impervious relation thereto, said member comprising a fluid cooled pipe coil, adjacent turns of said coil dening interstices pervious to the flow of material vaporized from said cathode pool.

23. In a vapor electric device, the combination of a casing comprising metallic parts, means connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material serving as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a fluid cooled pipe coil supported between said anode and said cathode in substantially insulated and arc impervious relation thereto, adjacent turns of said coil de- 13 iining interstices pervious to the ow of material vaporized from said cathode pool but impervious to arcing,

24. In a vapor electric device, the combination of a casing comprising metallic parts, means connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material serving as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a member pervious to the flow of material vaporized from said cathode pool but impervious to arcing supported between said anode and said cathode in substantially insulated relation thereto, and means comprising metallic shields forming arc impervious barriers across the gaps between said member and said anode and between said member and said cathode.

25. In a vapor electric device, the'combination of a casing comprising metallic parts, means connecting all the metallic parts of said casing in conductive relation to each other, a pool of vaporizable conductive material sewing as cathode disposed in said casing in conductive relation thereto, an anode disposed in said casing in insulated relation thereto, and means for preventing arcing between said anode and all said parts of said casing comprising a member impervious to arcing supported between said anode and said cathode in substantially insulated relation thereto, said member comprising a fluid cooled pipe coil, adjacent turns of said coil dening interstices pervious to the flow of material vaporized from said cathode pool, and means comprising 14 metallic shields forming arc impervious barriers across the gaps between said member and said anode and between said member and said cathode.

HAROLD WINOGRAD.

REFERENCES CITED The following references are of record in the file of this patent:

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